This invention relates to an improved apparatus for identifying the faulted phase during a phase-to-ground fault in high-voltage, three-phase, long-distance transmission lines such as for annunciating or recording the occurrence of such a fault or for single-pole trip and reclose protective relaying. The invention is herein illustratively described in presently preferred forms; however, it will be recognized that certain modifications and changes with respect to details of implementation may be made without departing from the essential features involved.
While there have been systems intended and operational to detect, annunciate or otherwise respond to line-to-ground faults in power transmission lines, most, if not all, of the phase identifying techniques have been unduly complex and expensive. Furthermore, such former systems were not altogether reliable or secure against false tripping or in consistently responding to faults. Such systems were based primarily upon abnormal line current flow in a transmission phase line attending a phase-to-ground fault.
An important object of the present invention is to provide a simplified, relatively low cost and reliable apparatus for the intended purpose. A related object is to provide such a system in which false tripping will be less likely than with prior systems and in which tripping or response to a phase-to-ground fault will occur substantially independently of concurrent load transients affecting the system. Also, the present invention will respond correctly to phase-ground faults occurring simultaneously on two of the three phase lines, whereas previous systems would not.
A specific object hereof is to devise such a system wherein specific location of the fault in terms of distance from the point of detection or installation of the responder apparatus is not critical to reliability of the response of the apparatus to a phase-to-ground fault.